9001 AIRPORT RD Geotech Report 2018-01-02 MF Import

i I Subsurface Ezplomrion. Ceologic Hma�d, and PreGmina7 Geotechnical Engineering Report Sro-lsle Skills Centu Addition Project and Site Ca^d+n°"S Everett, Wathington ( Lodgement Till I Lodgement till was encountered near the surface and extended to the full depths of our exploration borings. 1'he lodgement till generally consisted of ine,dium dense to very dease I gravelly silty sand. Scattered cobbles were encountered during drilling a°d °ften °�°r � till deposits. The lodgement till was deposited at the base of the Vashon-age glacial ice sheet and was subsequently overridden by several thousand feet of ice. Consequently, these materials ( are dense to very dense, possess high-strength, low-compressibility characteristics, and are relatively impermeable. The nearly impermeable nature of the till �`o�o f�e dgement till soils generally unsuitable for storm water infiltration. The upper po i were generally weathered and less dense, oxidized brown, and siltier than tl�e lower, unweathered ponions of the deposit. The lodgement till is suitable for d'uect support of foundations and pavement sections, although these soils aze susceptible to disturbance when wet due to the elevated silt contents. 4.2 Literatur�e�' We reviewed geologic data for We site based on the United States Geological Survey (USGS) Preliminary Su�ficial Geologie Map of the MukiUeo and Everett Quadrangles, Snohomish County, Washington, by Sarith, dated 1976. This map indicates that the near-surface sed"unents in the site viciniry consist of Vashon-age lodgement tili. Associated Earth Sciences, Inc.'s (AESI's) geologic findings aze in general agreement with those of the USGS. 43 Hydrology ' Ground water seepage was encountered in exploradon boring EB-2 at approximately 5.5 feet and in exploration boring EB-4 at approximately 6 feet below the surface. The ground water � encountered in the borings is indicative of a perched ground water condition. Perched ground water occws when surface water infiltrates down tluough relatively permeable soils, such as the fill or the weathered portions of the lodgement till, and becomes trapped or "pecched" atop � ,, compazatively impermeable soil horizou, such as the dense to very dense unweathered todgement till. It shouid be noted chat fluctuations in the level of the ground water may occur due to the time of the yeaz, on- and off-site usage, such as irrigatiou, and vaziations in rainfall. The quantiry and duradon of flow from excavations made into zones of perched ground water will vary depending on season, topography, and soil grain size. Based on the encountered subsurface conditions and ihe lack of wide-spread ground water, dewateTing acdvities wiil ;ikely not be required for trenching or subsurface excavations. Based on our preliminarY evaluation, storm water infiltration is not feasible on this site due to the presence of dense to very dense, relatively impermeable lodgement till at or near the II ground surface. ASSOCLI7E�F.1RTK SCT�NCES, WC. lune �I, wos Page 4 i Fcna-F�sol�3es-v.nlea,�200aozll�